This specification relates to optical components having small feature sizes.
A Fresnel lens is an optical component that can be used as a cost-effective, lightweight alternative to conventional continuous surface optical lenses (e.g., spherical lenses) in many applications. The refractive power of a continuous surface optical lens is provided by the optical interfaces at the continuous lens surfaces. To obtain a thinner lens (e.g., a Fresnel lens) having approximately the same refractive power as the continuous surface lens, lens material (e.g., glass) can be removed from the continuous surface lens while the optical interfaces of the continuous surface lens are maintained.
A practical implementation of an optical equivalent for a continuous surface lens, such as a Fresnel lens, is a multi-segment lens that has a finite prism pitch. For example, the smoothly curved lens surface of the continuous surface optical lens can be segmented, and the lens segments can each be approximated by a respective sloped lens facet and “collapsed” onto the same base plane. From a cross-section, each segment of the multi-segment lens forms a ridge above the planar base surface of the multi-segment lens, and each ridge has a sloped lens surface on one side and a nearly vertical draft surface on the opposite side. The sloped lens surface and the nearly vertical draft surface meet at the apex of the ridge. Each pair of adjacent ridges form a groove or valley above the planar base surface of the multi-segment lens, where the sloped lens surface of one ridge meets the draft surface of the adjacent ridge at the bottom corner of the groove or valley.
When designing a Fresnel lens, the pitch and the slopes of the lens surfaces and draft surfaces are carefully chosen to achieve a desired optical power, thickness, and transmission efficiency of the Fresnel lens.